The invention concerns a ratio controller, especially for fuel gas metering in gas burners, for example, forced-air burners.
In gas burners, a stipulated gas-air ratio must be set at the burners in order to ensure correct operation. The gas-air ratio must then be set independently of the load state. For burners that are in particular to be operated not only at nominal load, but also at partial load, this requires re-adjustment of the gas feed corresponding to air feed. The aim is to permit this with simple, robust and versatile devices.
In the design of gas heating installations, gas boilers and gas burners, system suppliers generally resort to vendor parts that can be incorporated into the overall system that are as much as possible problem-free. An effort is made, in particular, to assure that the assemblies, for example, appropriate ratio controllers, require no special control signals from other assemblies, in order to set the desired gas-air ratio correctly. Additional pressure taps or pressure lines, for example, from the burner to the ratio controller, represent undesirable limitations from the standpoint of the system supplier.
A ratio controller that regulates the gas feed to a burner is known from DE 197 40 666 C1. A ratio controller, to which a first pressure tap in the gas line and a second pressure tap in the combustion chamber are connected, is used for the desired adjustment of a stipulated gas-air ratio. Both pressure taps are provided with a throttle valve. Gas flows into the combustion chamber via the connection path between the two taps. A control pressure for the ratio controller is tapped between the throttle valve valves.
An additional pressure tap in the combustion chamber is often not present, so that use of this ratio controller is restricted.
Another ratio controller is known from EP 06 44 377 B1, which is formed by a pilot-controlled control valve provided with an actuating diaphragm. A pressure tap in the gas line leading to the burner, as well as two additional pressure taps in the air line leading from a blower to the burner, serve for pilot control. The two pressure taps in the air line record the pressure difference across a throttle valve location.
In this arrangement, an undesired hampering of air flow develops through the throttle valve location behind the forced-air burner. The pressure drop caused by the throttle valve must be overcome by the blower. This should be done in particular with respect to possible adjustments to different burner operating conditions, like loads, etc., as well as with respect to varying gas composition or the like.
With this as the point of departure, the task of the invention was to devise a simple and robust ratio controller without external pressure taps.